1. Field of the Invention
The present invention relates to a circuit apparatus for recognizing an earphone in a mobile terminal. More particularly, the present invention relates to a circuit apparatus for recognizing whether a pole of an earphone and a SEND/END key are input.
2. Description of the Related Art
A conventional mobile terminal supports a three-pole earphone in order to output a stereo sound source, and supports a multi-functional four-pole earphone in order to support voice communication and control a function of a mobile terminal. Recently, because both a three-pole earphone and a four-pole earphone are commonly used, the mobile terminal is able to determine use of the three-pole earphone and the four-pole earphone using a common use 3.5 inch ear jack that supports both the three-pole earphone and the four-pole earphone.
FIG. 1 illustrates a circuit diagram for recognizing an earphone in a conventional mobile terminal.
Referring to FIG. 1, the mobile terminal includes a baseband module 100 and a plurality of circuit devices for recognizing an earphone 130. The baseband module 100 includes a General Purpose Input Output (GPIO) 102 for receiving a detect/interrupt signal and a key sensing signal, and an Audio Block 104 for receiving an audio signal from a microphone 132.
A 3.5_DETECT end 140 of the mobile terminal maintains a low state when the earphone 130 is not connected, regardless of the number of poles of the earphone. More specifically, the 3.5 DETECT end 140 provides a voltage lower than a reference voltage 114 to a first comparator 112 if the earphone 130 is not connected. On the other hand, the 3.5 DETECT end 140 maintains a high state when the earphone 130 is connected in order to provide a voltage higher than the reference voltage 114 to the first comparator 112, thereby informing the baseband module 100 that the earphone 130 has been connected via the first comparator 112 and the first inverter 110.
An EAR_KEY end 142 transmits a different signal to the baseband module 100 depending on whether the connected earphone 130 is a three pole or a four pole earphone. More specifically, the EAR_KEY end 142 branches from a microphone line (i.e., EARMIC_P end 148) that receives a voice signal from the earphone 130 and transmits the voice signal to the Audio Block 104. When the four-pole earphone 130 is connected, the EAR_KEY end 142 transmits a different signal to the baseband module 100 depending on whether the SEND/END key is input.
That is, when the earphone 130 is connected to the mobile terminal, a bias voltage is supplied to the EARMIC_P end 148 by a MIC_BIAS 144 and a pull-up resistor R1 146, and accordingly, a bias voltage is supplied to the EAR_KEY end 142. At this point, when the connected earphone 130 is a three-pole earphone, the EARMIC_P end 148 contacts a GND of the earphone, so that the EAR_KEY end 142 becomes a low state to provide a voltage lower than a reference voltage 124 to a second comparator 122. In contrast, when the earphone 130 connected to the mobile terminal is a four-pole earphone, the EARMIC_P end 148 is connected to a microphone resistor of the earphone 130 and the EAR_KEY end 142 is placed into a voltage state that is higher than the reference voltage. Thus, the EAR_KEY end 142 provides a voltage higher than the reference voltage 124 to the second comparator 122 thereby informing the baseband module 100 that a four-pole earphone has been connected via the second comparator 122 and a second inverter 120. Therefore, the baseband module 100 is able to determine whether a currently connected earphone is a three-pole or four-pole earphone.
In addition, while the four-pole earphone 130 is connected to the mobile terminal and provides a voltage higher than the reference voltage 124 to the second comparator 122, when the SEND/END key of the four-pole earphone 130 is input, the EAR_KEY end 142 is connected with GND and becomes a low state. In the low state, a voltage lower than the reference voltage 124 is provided to the second comparator 122 so that the baseband module 100 is able to recognize that the SEND/END key is input and perform a corresponding operation.
As described above, in the conventional mobile terminal, the EAR_KEY end 142, which discriminate whether a connected earphone is a three-pole or a four-pole earphone and recognizes input of the SEND/END key, branches from a microphone line. That is, the EAR_KEY end 142 branches from the EARMIC_P end 148 that receives a voice signal from the earphone. In this case, the EAR_KEY end 142 and the EARMIC_P end 148 may influence each other.
Furthermore, in the conventional mobile terminal, noise from Time Division Multiple Access (TDMA) Radio Frequency (RF) coupling and noise from power circuitry is detrimental to the EAR_KEY end 142 due to the wiring of the EAR_KEY end 142. The detrimental TDMA noise to the EAR_KEY end 142 in the structure of FIG. 1 has an influence on the EARMIC_P end 148, and consequently causes interference to a voice of a user input from a microphone 132 of the earphone 130.
Accordingly, a structure in which the EARMIC_P end 148 is not influenced by the EAR_KEY end 142 in the circuit apparatus of the mobile terminal for recognizing the number of poles of an earphone is needed.